Vehicle drive axles typically include a pair of axle shafts for driving vehicle wheels. The drive axle uses a differential to control input speed and torque to the axle shafts. Under ideal conditions, when the vehicle is driven along a straight path under good road conditions, the vehicle wheels will be turning at approximately the same speed and the torque will be equally split between both vehicle wheels. When the vehicle negotiates a turn, the outer wheel must travel over a greater distance than the inner wheel. The differential allows the inner wheel to turn at a slower speed than the outer wheel as the vehicle turns.
A typical differential includes a differential housing that is driven by a final axle input gear, such as a ring gear. A differential spider is fixed to the differential housing and has four (4) support shafts, orientated in the shape of a cross, with each shaft supporting one differential pinion gear. The differential pinion gears are in meshing engagement with side gears that are splined to the axle shafts.
When the vehicle is driven in a straight path, the ring gear, differential housing, spider, and differential pinion gears all rotate as one unit to transfer power to the axle shafts. There is no relative movement between the differential pinion gears and the side gears. When the vehicle turns, the differential pinion gears rotate on their respective shafts to speed up the rotation of one axle shaft while slowing rotation of the other axle shaft.
Under certain driving conditions, such as wet or icy road conditions for example, standard drive axle differentials can cause wheels to slip and can ultimately lose capability to transmit torque. Often, a traction aid device is incorporated into a drive axle or differential to produce resistance to wheel slip. Optionally, a locking mechanism is incorporated into the differential to eliminate slip by providing a full differential lock condition. These traction aid devices and locking mechanisms require modification of existing components and/or require components to be added to the drive axle. This significantly increases cost for the drive axle. Additionally, these traction aid devices and locking mechanisms usually require hydraulic, electric, or pneumatic actuation, which increases complexity as well as further increasing cost.
There is a need for a differential that provides maximum traction during low traction conditions, but which does not require additional hydraulic, electric, or pneumatic traction aiding devices.